http://www.superbestaudiofriends.org/index.php?threads/source-av-meet-impressions.5748/#post-189887
Sennheiser 600 w/ Dekoni Fenestrated Sheepskin Pads - @brencho & @Bill-P are right, just add pads and be done. Balances out the leaner signature and adds some much needed bass that doesn't bleed into the mids.

"HD600wDekoni Fenestrated Sheepskin Pads - These with no front foam over the driver. Adds a bit of bass to the hd600, balances out the upper mid bump a bit, and sounds pretty good. Not sure these pads are all that necessary with my Zana Deux but they're also way more comfortable than the stock pads because my ears don't brush up against the foam like with stock pads. They also seem to have more structural integrity and will hold up better to use. However, on the hd650 they will be too much, these pads will prob make the bass issue of the hd650 worse and make them even darker sounding."

Shared this because a lot of people here owns the HD6XX, and since the HD6XX are almost exactly the same as the HD650, it's important to know this.

I bought the fernestrated sheepskin earpads(The most expensive ones), and i can honestly say i'm very dissapointed. Not only are they less comfortable than the stock earpads, but they also defy the actual purpose of the headset, as they make the headset more noicecancelling. As you probably know, the headsets mentioned are not headsets focused on noice cancelling, but being open back and free. The earpads also make smaller holes for your ear, so if you have big ears, you should not even think about buying any of these earpads. Soundwise i don't hear alot of difference between the two. Maby just a little more base in the Dekoni earpads, as the deep sounds get channelled through to your ears better, because of the way they are closed up and tight. All i can conclude is, that you shouldn't go for the fernestrated sheepskin earpads, as they are crap.

Don't worry too much, sound is subjective, probably you don't like this kind of sound. A lot of people dislike the HD600-family because of the laid-back sound, the "veil" (after a lot of listening on them, I don't think there's a veil, but they don't have the artificial brightness that some others have), the not-too-great soundstage (it's not bad, but not mind-blowing like some AKG models), the lack of sub-bass (quite common in open-back headphones)... They're not for everyone, no headphone is "good" for everyone.

Monolith M1060 look great, I'd suggest you to get into the HE4XX but the drop finished SO FAST (maybe because they're awesome price-performance, I hope they are because I got my pair). Some other completely different options:

There's a lot of great options in the sub-$100 price range, if you don't wanna go big and spend $300 on the M1060. If you do, please share some thoughts because I'm really interested on these :) I'll share you one review I saw, seems very interesting: https://www.reddit.com/r/headphones/comments/6b8cqf/not_another_monoprice_m1060_review/